The present invention generally relates to snack products comprising a high concentration of soy protein and processes for making such high protein snack products. More particularly, the present invention relates to semi-chewy or crisp high soy protein-containing snack products having a fruity or savory flavor.
In recent years, it has become common for consumers to choose foods that are convenient and tasty. However, convenient or ready-to-eat foods tend to be nutritionally unbalanced as they are high in fat and carbohydrates, and low in dietary fiber and protein. In particular, it is appreciated that the high fat and calorie load and low dietary fiber level of these convenient foods can contribute to obesity and various chronic diseases, such as coronary heart disease, stroke, diabetes, and certain types of cancer.
In response to the results of recent research showing the possible negative effects of particular foods, consumers are becoming more health conscious and monitoring their food intake. In particular, since animal products, like red meats, are the only main dietary source of cholesterol and may contain high levels of saturated fats, health professionals have recommended that consumers significantly reduce their intake of red meats. As a substitute, many consumers are choosing fish and poultry, but vegetable products, such as vegetable proteins, are also growing in popularity.
Generally, vegetable protein is eaten in the form of beans or other natural products, but enriched sources such as flour, concentrates, and isolates of defatted oilseed, especially soy, have been developed for use as food ingredients.
Texturized vegetable protein products for use in food are known in the art and are typically prepared by heating a mixture of protein material along with water under mechanical pressure in a cooker extruder and extruding the mixture through a die. Upon extrusion, the extrudate generally expands to form a fibrous cellular structure as it enters a medium of reduced pressure (usually atmospheric). Expansion of the extrudate results from inclusion of soluble carbohydrates, which reduce the gel strength of the mixture. The extrudates are then used to form other products such as vegetable meat analogs. Extrusion methods for forming textured protein meat analogs are well known and disclosed, for example, in U.S. Pat. No. 4,099,455.
Soy protein products can be good substitutes for animal products because, unlike some other beans, soy offers a “complete” protein profile. Soybeans contain all the amino acids essential to human nutrition, which must be supplied in the diet because they cannot be synthesized by the human body. Additionally, soybeans have the highest protein content of all cereals and legumes with around 40% protein. Soybeans also contain about 20% oil and the remaining dry matter is mostly carbohydrate (35%). Typically, soybeans contain about 35% (by weight) protein, 17% (by weight) oil, 31% (by weight) carbohydrates, and 4.4% (by weight) ash.
Suitable soy protein products include soy flakes, soy flour, soy grits, soy meal, soy protein concentrates, soy protein isolates, and mixtures thereof. The primary difference between these soy protein materials is the degree of refinement relative to whole soybeans.
Soy flakes are generally produced by dehulling, defatting, and grinding the soybean and typically contain less than 65% (by weight) soy protein on a moisture-free basis. Soy flakes also contain soluble carbohydrates, insoluble carbohydrates such as soy fiber, and fat inherent in soy. Soy flakes may be defatted, for example, by extraction with hexane. Soy flours, soy grits, and soy meals are produced from soy flakes by comminuting the flakes in grinding and milling equipment such as a hammer mill or an air jet mill to a desired particle size. The comminuted materials are typically heat treated with dry heat or steamed with moist heat to “toast” the ground flakes and inactivate anti-nutritional elements present in soy such as Bowman-Birk and Kunitz trypsin inhibitors. Heat treating the ground flakes in the presence of significant amounts of water is avoided to prevent denaturation of the soy protein in the material and to avoid costs involved in the addition and removal of water from the soy material. The resulting ground, heat treated material is a soy flour, soy grit, or a soy meal, depending on the average particle size of the material. Soy flour generally has a particle size of less than about 150 μm. Soy grits generally have a particle size of about 150 to about 1000 μm. Soy meal generally has a particle size of greater than about 1000 μm.
Soy protein concentrates typically contain about 65% (by weight) to about 85% (by weight) soy protein, with the major non-protein component being fiber. Soy protein concentrates are typically formed from defatted soy flakes by washing the flakes with either an aqueous alcohol solution or an acidic aqueous solution to remove the soluble carbohydrates from the protein and fiber. On a commercial scale, considerable costs are incurred with the handling and disposing of the resulting waste stream.
Soy protein isolates, which are more highly refined soy protein materials, are processed to contain at least 90% (by weight) soy protein on a moisture free basis and little or no soluble carbohydrates or fiber. Soy protein isolates are typically formed by extracting soy protein and water soluble carbohydrates from defatted soy flakes or soy flour with an alkaline aqueous extractant. The aqueous extract, along with the soluble protein and soluble carbohydrates, is separated from materials that are insoluble in the extract, mainly fiber. The extract is typically then treated with an acid to adjust the pH of the extract to the isoelectric point of the protein to precipitate the protein from the extract. The precipitated protein is separated from the extract, which retains the soluble carbohydrates, and is dried after being adjusted to a neutral pH or is dried without any pH adjustment.
It is well known that these vegetable products, such as soy protein products, contain no cholesterol. For decades, nutritional studies have indicated that the inclusion of soy protein in the diet actually reduces serum cholesterol levels in people who are at risk. Further, the higher the cholesterol level, the more effective soy proteins are in lowering that level.
Despite all of the above advantages, it is well known that by supplementing foods with increased levels of dietary fiber and protein, taste can be seriously compromised. More particularly, protein sources, such as soy flour, can produce objectionable off-flavors in the finished products. For example, many consumers complain that high protein foods, like those supplemented with soy protein, taste chalky and bland.
In addition to the challenges associated with improving taste, it is known that increasing a food's protein level typically results in the loss of the desirable product texture that consumers expect. This is especially true for snack foods. The loss of desirable texture typically results in products, such as high protein and fiber health bar snacks, that are described by consumers as having an unpleasant stickiness, grittiness, or dryness. Instead of improving texture, current attempts to solve textural problems merely hide unpleasant textural characteristics. Attempted solutions include coating products with materials that are high in fat. Unfortunately, these “fixes” are only temporary, as shortly after the initial bite or product breakdown, the true nature of the product's texture becomes apparent. While the loss of textural quality is appreciated by those skilled in the art, the complex interactions that give rise to poor textures are little understood.
Additionally, there is a problem with long-term storage of these protein-enriched foods due to the growth of microorganisms. The growth of microorganisms, especially bacteria, is closely associated with the water activity level, or availability of free water, of a food product. When a bacterial cell is placed in a solution with low water activity, the cell dehydrates and bacterial growth is inhibited. According to the principles of thermodynamics, water activity is the driving force behind dehydration. Furthermore, yeasts and molds tend to be extremely resistant to water activity. They are particularly effective in obtaining water even under lower water activity conditions than bacteria.
As is evident from the foregoing, a need exists in the industry for a convenient, ready-to-eat food product that provides a high concentration of protein and has an acceptable taste and texture. Additionally, it would be beneficial if the food product could significantly reduce the growth of microorganisms so that the product is shelf stable and can be stored for prolonged periods of time for retail sale.